National: Outsourcing: The company: Big profits but some questions

The Minnesota-based UnitedHealth has already become a key adviser to primary care trusts (PCTs) on commissioning health services and operating bids to run GP practices. Earlier this month it beat Bupa and Humana, another US health insurer, to win the contract from the health department to advise PCTs.

The decision follows successful bids to run two GP practices in Derbyshire in 2006 and three practices in central London in 2008, taking over from the Brunswick Group. In April the company announced a 21% increase in profits for the first three months of the year to $1.2bn (pounds 784m).

United said it brought high level management expertise and efficient provision of services to the UK health service but it has faced accusations of overcharging and malpractice in a series of legal suits.

In 2008 it agreed to pay $50m after the New York attorney general Andrew Cuomo sued the company "as part of a broad probe into how insurers pay doctors and hospitals that aren't in the companies networks".

According to Cuomo, UnitedHealth's Ingenix unit operated a "defective and manipulated database" to set charges for medical services.

Its California subsidiary was fined a record $3.5m in the same year for mishandled claims against patients and doctors. In 2006 The UnitedHealth chief executive William McGuire resigned after an investigation "concluded he had received stock option grants 'likely backdated' to allow insiders to maximise financial gains."